When you want to make an image collage, you usually gather a collection of images and bring them into Photoshop on separate layers. From there, you can resize the individual images on the layers with Transform commands, if necessary. Then you can add layer masks and use them to hide parts of the image you don't want.
Let's say you want to use three images to make a 4.5 × 3-inch collage at 300 ppi in CMYK mode for a magazine. Figure 16.13 shows the three original images that will be used in the collage.
Here are the typical steps you might follow to make a three-image collage:
Create a new Photoshop document by choosing FileNew. Make a 4.5 × 3-inch, 300 ppi, RGB document (it will be changed to CMYK later). Leave this document open.
Click the Maximize button at the top of the Photoshop Application Frame to make the workspace as large as possible. You can click the Minimize button if you need to temporarily get it out of the way.
Open the three images and make sure they have at least enough size and resolution to maintain their quality at their final size in the collage. See Chapter 5 for resizing and resolution.
Click the Arrange Documents ...